Patient match instrument

ABSTRACT

A patient matched instrument for a patient&#39;s femur is disclosed. The instrument includes a body having a cutting slot and a patient matched surface that mates with the patient&#39;s trochlear groove, a first leg portion extending from the body, a second leg portion extending from the body; and each leg portion has a contacting pad for tangential contact with the patient&#39;s femoral medial and lateral condyles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/671,758, filed 15 Jul. 2012, of U.S. Provisional Application No.61/681,440, filed 9 Aug. 2012, and of U.S. Provisional Application No.61/715,562, filed 18 Oct. 2012. The disclosure of each prior applicationis incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to surgical instruments andmethods for the treatment of bones or joints, in some instances surgicalinstruments that are matched to a particular patient's anatomy, aredescribed herein. Also described are methods of designing and using suchsurgical instruments.

Conventional patient-matched instruments are provided with largesurfaces that are configured to conform to a patient's unique anatomy.Successful surgical outcomes depend on the ability of patient-matchedinstruments to provide a reproducible, “confident” 3D-fit between thepatient-matched instrument and the anatomy that they are designed torest against. If there is any doubt by an end user that apatient-matched instrument fits well upon repeated engagement with apatient's unique anatomy, or if the instrument appears to fit well withthe patient's anatomy in multiple spatial orientations with respect tothe anatomy, the instrument is typically discarded, and the surgery iscarried out with the use of conventional, non-patient specificinstruments.

To date, at least some patient-matched surgical instruments for use intotal knee arthroplasty have employed anatomy-contacting surfaces thatare substantially “negatives” of distal femoral and proximal tibialarticular joint surfaces. The anatomy-contacting surfaces are generallylarge surface areas that conform in a continuous manner to substantialareas of a patient's anatomy. In some instances, the custom surgicalinstruments are provided by obtaining 3D image data of the patient'sanatomy (e.g., via an MRI scan), segmenting the 3D image data to clearlydelineate surfaces of the bony and/or cartilegeneous anatomy fromsurrounding tissues, converting the segmented data to a computer modelvia CAD or other software, performing one or more optional secondaryprocesses (e.g., smoothing functions), using a computer model tocustomize one or more surfaces of an instrument to the patient'sanatomy, and manufacturing the custom instrument such that it is adaptedto conform to the patient's anatomy in a single spatial orientation.

In at least some current practices, substantially all portions of thejoint anatomy shown in each 3D image data slice are segmented andconventional patient-matched instruments are provided withanatomy-contacting portions that contact substantially continuous areasof the patient's anatomy. Such anatomy-contacting portions have largecontinuous surface areas of contact with the patient's bone andcartilage, and therefore, it is critical that the engineers or automatedprograms creating the patient-matched instruments maintain a high levelof accuracy and precision throughout each step of the entiresegmentation process. Even if only one or two points onanatomy-contacting surfaces of a patient-matched instrument areinaccurate, misaligned, or otherwise misrepresent the true uniqueanatomy of the patient, the patient-matched instrument may not fit well,sit proud, teeter, wobble, or may not fit at all. In such instances, anend user is less likely to use the instrument. In many cases, poorpatient-matched instrument fit may be attributed to even a few minorerrors in the segmentation process.

SUMMARY OF THE INVENTION

The various embodiments of the present invention described below andshown in the Figures provide a patient matched instrument that isdesigned to provide improved repeatability and reproducibility over theprior art. The patient matched instrument includes a patient matchedsurfaces that mates with a patient' s trochlear groove and twocontacting pads for tangent contact with the patient's femoral condyles.The patient matched instrument incorporates design features thatencourage consistent placement and accurate placement.

Further areas of applicability of the invention will become apparentfrom the detailed description provided hereinafter. It should beunderstood that the detailed description and specific examples, whileindicating the particular embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which is this case is a group of sketchesprepared by the inventor and, which are incorporated in and form a partof the specification, illustrate the embodiments of the invention andtogether with the written description serve to explain the principles,characteristics, and features of the invention. In the drawings:

FIG. 1 shows a side perspective view of a patient matched instrumentmounted on a left femur.

FIGS. 2A and 2B show an inferior-superior view of the patient matchedinstrument of FIG. 1.

FIG. 3 shows an anterior-posterior view of the patient matchedinstrument of FIG. 1.

FIG. 4 shows a bottom perspective view of the patient matchedinstrument.

FIG. 5 shows a bottom view of the patient matched instrument.

FIGS. 6A and 6B show a side view of two embodiments of the patientmatched instrument.

FIG. 7 is an exemplary illustration of a human right-side femur attachedto a tibia by the anterior and the posterior cruciate ligaments.

FIG. 8 is an expanded view of a human right-side knee joint in a bentposition.

FIG. 9 illustrates the anterior trochlear sulcus which may be used todetermine the AP axis.

FIG. 10 illustrates an embodiment of the patient instrument with awindow to view the AP axis.

FIGS. 11 a and 11 b illustrate an embodiment with a grid opening to viewthe AP axis.

FIGS. 12-13 illustrate an embodiment having an anterior ridge extension.

FIGS. 14-19 illustrate an embodiment having surface contact confirmationslots.

FIGS. 20-24 illustrate a distal trochlea notch grip.

FIG. 25 illustrates an embodiment of the patient matched instrumenthaving tangent contact paddles.

FIGS. 26 and 27 graphically illustrate the consistency and accuracyprovided by the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description of the depicted embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Embodiments of the present invention provide a patient matchedinstrument that is designed to provide improved repeatability andreproducibility over the prior art. FIG. 1 illustrates a patient matchedinstrument 200 placed on a femur 2. The patient matched instrument 200is used to make a distal cut in knee arthroplasty. The patient matchedinstrument 200 includes a body 202. A first leg portion 206 and a secondleg portion 208 extend from the body 202. The body includes a cuttingslot 210 and one or more pin bosses 212 are located on each leg portion206,208. In some embodiments, the patient matched instrument 200 alsoincludes pin mounts 214. In use, the femur 2 is exposed via surgicalincision. The patient matched cutting block 200 is placed on the femur 2and located in a home position. Pins (not shown) are inserted into thepin bosses 212. Pins may be inserted into the pin mounts 214. A sawblade 4 (FIG. 2B) is reciprocated in the cutting slot 210 to remove bonefrom a distal end of the femur 2.

In some embodiments, the patient matched instrument 200 may include avisual indicator 216. In the depicted embodiment, the visual indicator216 is formed by a groove, however, the visual indicator 216 also may beformed by other shapes or by other methods, such as painting orprinting. As an example, the visual indicator 216 may align with theanterior-posterior (AP) axis or Whiteside's line of the femur 2. Asanother example, the visual indicator 216 may indicate the mechanical oranatomic axis of the femur 2.

FIGS. 2A and 2B illustrate the patient matched instrument 200 mounted onthe femur 2. The femur 2 has a medial condyle 106, a lateral condyle104, and an intercondylar notch 21. Optionally, the patient matchedinstrument 200 may include a window 220. The window 220 allows anoperator to see a saw blade 4 as it progresses in making the distal cut.As an example, the saw blade 4 may be seen in front of the intercondylarnotch 21 between condylar portions 104,106 of the femur 2. In someembodiments, the patient matched instrument 200 includes one or moreapertures 222. The aperture 222 may take any shape. For example, theaperture 222 may be square, rectangular, cylindrical, or trapezoidal.The patient matched instrument 200 includes a front surface 204

The patient matched instrument 200 includes the first leg portion 206and the second leg portion 208. Each leg portion 206,208 includes one ofthe pin bosses 212. In some embodiments, each leg portion 204, 206extends anteriorly in front of each condyle 104, 106. Each leg portion206,208 may have a radiused face 224.

In some embodiments, the patient matched instrument 200 includes a guide230. The guide 230 may be used to check for general alignment. Forexample, the guide 230 may align with the epicondylar axis, and a usermay inspect the guide 230 compared to the epicondylar axis to check forgeneral alignment of the patient matched instrument 200. The guide 230,if included, is also functional as it connects the first leg portion 206to the second leg portion 208 for structural reinforcement. In thedepicted embodiment, the guide 230 is substantially square and has athickness of about 3 mm. Of course, other shapes, such as round, arepossible, and also other dimensions are possible. For example, the guide230 may have a cross-sectional diameter or width ranging from about 2 mmto about 15 mm, with a preferred range of about 3 mm to about 6 mm.

As shown in FIG. 3, the patient matched instrument 200 may include oneor more additional fixation holes 236 to temporarily affix the patientmatched instrument 200 to the femur 2. In some embodiments, the fixationhole 236 is angled relative to the cutting slot 210. For example, thefixation hole 236 may be angled from about 15 degrees to about 75degrees. In the depicted embodiment, the fixation hole 236 is angled atabout 45 degrees relative to the cutting slot 210.

FIG. 4 illustrates the patient matched instrument 200 having a patientmatched surface 240, a first contact pad 250, and a second contact pad252. The patient matched surface 240 may be substantially defined by sixboundary conditions 8, 10, 12, 14, 16, and 18 (outlined in FIG. 4 forvisibility). In general, the patient matched surface 240 iscustom-designed and manufactured to match the shape of and mate with aportion of a patient's trochlear groove. The first and second contactpads 250,252 are each generally planar and formed on each respective legportion 206,208. The first and second contact pads 250,252 may be offsetfrom one another in an anterior-posterior direction for varus/valgusconstraint. The first and second contact pads are constructed andarranged to contact the utmost distal portions of the condyles 104,106.Due to the nature in which imaging data is obtained (i.e., 2 mm slicesin a sagittal plane) and 3D bone anatomic models are produced, thecombination of the trochlear groove contact in combination with thedistal condyle contact provides a custom cutting block is the highlyreproducible and repeatable. As more accurate data is available as tothe utmost distal point of each condyle 104, 106, in some embodimentsthe contact pads 250,252 are the primary references and any othercontact portion, such as in the trochlear groove, is secondary. This maybe of significance for geometric tolerancing. Each of the first andsecond contact pads 250,252 may provide line contact, area contact, aplurality of contact points, or a single point of contact.

As best seen in FIG. 5, the leg portions 206, 208 may be of differentlengths. Also, the boundary 8 (described in greater detail below) has astraight edge appearance but need not have one.

In the embodiment depicted in FIG. 6A, the first and second contact pads250, 252 are generally parallel to the cutting slot 210 and/orsubstantially perpendicular to the mechanical axis. Those of ordinaryskill in the art would understand that other arrangements are possible.For example, as shown in FIG. 6B, the first and second contact pads maybe designed to contact other and/or additional portions of condyles 104,106 at an angle relative to the cutting slot 210 and/or the mechanicalaxis.

FIGS. 7 and 8 show exemplary views of a normal, intact knee joint. Byway of background, a human knee joint includes two cruciate ligamentswhich are located in the center of the knee joint. As shown in FIG. 8,these two ligaments, referred to in the art as the anterior cruciateligament (ACL) 22 and the posterior cruciate ligament (PCL) 24, areprimary stabilizing ligaments of the knee. The ACL 22 attaches at itsdistal end 26 to the tibia 30, and passes obliquely upward into theinner and back part 32 of the lateral condyle 104 of the femur 2 forattachment at the proximal end. Attachment of the ACL 22 to the femur 2stabilizes the knee joint along the anterior-posterior direction andprevents the femur 2 from sliding backwards on the tibia 30 (or thetibia from sliding forward on the femur).

In some embodiments, the first boundary condition 8 of the patientmatched surface may be designed to not extend far back to impinge uponthe cruciate attachments or the ligaments themselves. Therefore, thefirst boundary condition of a patient matched surface may be defined tobe about 2 to about 13 mm from the point of attachment of the ACL 22 orthe PCL 24 to the patient's femur 2. More specifically, as illustratedin FIG. 8, the first boundary condition 8 may be from about 3 mm toabout 6 mm from the point of attachment 20 of the ACL 22 or PCL 24. Inother words, there is about 2 mm to about 13 mm distance between thefirst boundary condition 8 and the attachment 20 of the ACL 22 or PCL24. Alternatively, the first boundary condition of a patient matchedsurface 8 is within the intercondylar notch 21 but of a sufficientdistance above where the ACL 22 or PCL 24 exits.

The second boundary condition 10 may be defined approximately at or neara superior edge 100 of an end of natural cartilage 102. In someembodiments, the patient matched surface 240 may extend slightly overthe superior edge 100 to “hook” upon it. In other words, the secondboundary condition 10 may have a lip to engage the superior edge 100.The third boundary condition 12 may be approximately at a top ridge ofthe lateral condyle 104. The fourth boundary condition 14 may beapproximately at a top ridge of the medial condyle 106. The fifth andsixth boundar condition 16, 18 are angled upward and away from thecondyles 104, 106 to provide clearance. The four boundary conditions 8,10, 12, 14 as described above, may substantially define the perimeter orouter edges of the patient matched surface 240. However, the patientmatched surface 240 need not be defined by any one of the four boundaryconditions. Alternatively, the patient matched surface may be defined byany one of or any combination of the four boundary conditions. Ofcourse, the perimeter or outer edges of individual patient matchedsurfaces may differ depending on the unique anatomic characteristics ofan individual patient's femur.

Alternatively, a portion of the perimeter of the patient matched surface240 may be defined by intersecting the cutting plane with a trochleargroove of the anatomic model. The resulting edge provides a generaldefinition of the boundary condition edge 8. In other words, the patientmatched surface 240 may be defined by intersecting boundaries of theanatomic model and the cutting plane. For example, the patient matchedsurface 240 is defined in a CAD model of the patient's anatomy bycreating the distal cutting plane of the femur and defining the edgebetween cutting plane and the trochlear groove of the anatomic model.

As best seen in FIG. 9, a user may use points P on the femur 2 togenerate a line W. Line W is indicative of the AP axis, a featurecommonly used as a reference in knee surgery. As an example, a user mayuse a bovie to generate the points P and the line W.

FIG. 10 illustrates a patient matched instrument 300. The patientmatched instrument has a passage 310. The passage 310 is customized foreach individual patient. For example, an engineer or automated softwarelandmarks low points of an anterior sulcus by creating points on a bonemodel created from imaging data in a modeling or imaging software. Inone particular embodiment from about 4 to about 10 points are created onthe bone model. The created points are connected with a line in themodeling or imaging software. This line forms the midline of thepositive or negative AP line feature on the patient matched instrument.When the patient matched instrument is placed on the bone, the user canview the AP axis through the passage 310 for visual confirmation as tocorrect placement. Alternatively, the user can use the passage to tracethe AP axis for use as a guide when the patient matched instrument isplaced on the bone.

FIG. 11 a illustrates a patient matched instrument 400. The patientmatched instrument has a first cross-member 410, a second cross-member420, and a third cross-member 430. The patient matched instrument 400could have additional or fewer cross-members. The cross-members 410,420, 430 form openings 450. The user can view the AP axis along thefirst cross-member 410 for visual confirmation as to correct placement.Additionally, a user can use openings 450 to visualize and confirm thatcross-members 420,430 contact bone.

FIG. 11 b illustrates a variation of the embodiment shown in FIG. 11 a.In the depicted embodiment, the patient matched instrument 400′ has afirst cross member formed by a lateral member 461 and a medial member463. The lateral and medial members 461, 461 are spaced apart to form aspace 465. The user can view the AP axis through the space 465 forvisual confirmation as to correct placement. Alternatively, the user canuse the space 465 to trace the AP axis for use as a guide.

In some embodiments, the patient matched instrument 400 may include ananterior ridge extension 460. The anterior ridge extension 460 includesa first ear 462 and a second ear 464. In some embodiments, the anteriorridge extension 460 may include only the first ear 462 or the second ear464. The anterior ridge extension 460 creates additional contact alongboth medial and lateral portions of the femoral anterior ridge.

Alternative embodiments of the anterior ridge extension are shown inFIGS. 12 and 13. In the depicted embodiment, the patient matchedinstrument 500 includes an anterior ridge extension 510. The anteriorridge extension 510 includes a first ear 514 and a second ear 512. Insome embodiments, the anterior ridge extension 510 may include only thefirst ear 514 or the second ear 512. The anterior ridge extension 510creates additional contact along both medial and lateral portions of thefemoral anterior ridge.

FIGS. 14-19 an embodiment having surface contact confirmation slots thathelp determine proper placement of a patient matched instrument as avisual check to ensure correct placement. In the depicted embodiment,the patient matched instrument 600 has a medial surface contactconfirmation slot 610 and a lateral surface contact confirmation slot612. The slots 610, 612 cut out of the distal paddles of the patientmatched instrument denote a point that the distal femur makes contactwith a tangent surface of the patient matched instrument. A user, suchas surgeon, may place the patient matched instrument on the femur, viewthe patient matched instrument laterally and medially to verify that theslot outline lines up with the point where the patient matchedinstrument and bone meet. Although slots are shown in the depictedembodiment, those having ordinary skill in the art would understand thatthe confirmation feature could be negative (such as the slot) orpositive. Further, instead of slots, other shapes, such as arrows orcircles, may be used.

FIGS. 17-19 illustrate a variation of the embodiment shown in FIGS.14-16. In the depicted embodiment, the patient matched instrument 650includes not only medial and lateral slots 652, 658, but also distalslots 654, 656. In some embodiments, all or some of the slots 652, 654,656, 658 may include color to increase visibility. For example, some ofthe slots may be colored red or yellow. The slots 652, 654, 656, 658 aresized and shaped to line up with only one point. A user view the femurposteriorly and sagittally to confirm the slots where the patientmatched instrument contacts bone.

FIGS. 20-24 illustrate a distal trochlea notch grip. The notch grip is aportion of the patient matched instrument that is extended to contactand conform to the distal trochlea. In a first embodiment, the patientmatched instrument 700 includes a distal trochlea notch grip 712. Insome embodiments, the patient matched instrument 700′ has a frangibledistal trochlea grip 712′ that is constructed and arranged to break atan area 714. The part is frangible after fixation to eliminateinterference with resection. In some embodiments, the distal trochleanotch grip is combined with the anterior ridge extension to aid incapturing the patient matched instrument in two relatively opposedlocations.

The second embodiment, depicted in FIGS. 23-24, illustrates a patientmatched instrument 750 with a somewhat wider and larger distal trochleanotch grip 752 than the one shown in FIGS. 20-22. As with the firstembodiment, the distal trochlea notch grip 752 may be frangible in someinstances.

FIG. 25 illustrates an embodiment of the patient matched instrument 800having paddles 810. The paddles 810 provide angled, tangent contact witheach femoral condyle to provide additional rotational stability.

FIGS. 26 and 27 graphically illustrate results of lab testing of thedisclosed embodiments. The protocol consisted of three operatorsperforming three to five placement of each block design on a cadaverbone. Three degrees of freedom were measured with a computer assistedsurgery (CAS) system for each individual placement. Specifically, thesewere: (1) varus/valgus rotation angle; (2) flexion/extension rotationangle; and (3) internal/external rotation angle. The standard deviationof all placements for a given block design was calculated for eachdegree of freedom. FIGS. 26 and 27 illustrate that the present invention(named “PFJ+Points” on the graphs) had the lowest standard deviation ofall tested devices. Further, FIG. 27 illustrates that reducing the PFJcontact portion and replacing it with a somewhat truncated contact withseveral points (named “Points” on the graphs) was less than optimal butnot necessarily unacceptable. There may be a threshold where thearea/point contact trade off becomes “even” (as determined by theconstraint provided), and as such it may be best described as a “pointdensity” (points per unit area) rather than a specific number of pointsthat is optimal. Also, that point density could vary over the surface.In some embodiments, full PFJ-area contact may be replaced by a range ofpoint contact densities that are functionally equivalent or superior tofull area contact. As an example, the range may be about 5 points/cm̂2 toabout 30 points/cm̂2.

The term “substantially” as used herein may be applied to modify anyquantitative representation which could permissibly vary withoutresulting in a change in the basic function to which it is related. Forexample, the contacting pads are disclosed as being substantiallyperpendicular to the mechanical axis and may permissibly have somevariation from being truly perpendicular and still be within the scopeof the invention if the function of the contacting pads are notmaterially altered.

In view of the foregoing, it will be seen that the several advantages ofthe invention are achieved and attained.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. For example, while FIG. 1illustrates pin bosses that receive pins other structure and/or methodsmay be used to temporarily affix the patient matched instrument to thefemur. Thus, the breadth and scope of the present invention should notbe limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims appendedhereto and their equivalents.

What is claimed is:
 1. A patient matched instrument for a patient's femur having a trochlear groove, a medial condyle, and a lateral condyle, the instrument comprising: a. a body having a cutting slot and a patient matched surface that mates with the patient's trochlear groove; b. a first leg portion extending from the body; c. a second leg portion extending from the body; and d. wherein each leg portion has a contacting pad for tangential contact with the patient's femoral medial and lateral condyles.
 2. The instrument of claim 1, the body further comprising a visual indicator.
 3. The instrument of claim 1, the body further comprising a window.
 4. The instrument of claim 1, the body further comprising apertures.
 5. The instrument of claim 1, wherein each leg portion further comprises at least one pin boss.
 6. The instrument of claim 1, further comprising a guide.
 7. The instrument of claim 1, wherein the patient matched surface of the body has six boundary conditions.
 8. The instrument of claim 1, wherein the first leg portion has a different length from the second leg portion.
 9. The instrument of claim 1, wherein the contacting pads are substantially perpendicular to the mechanical axis.
 10. The instrument of claim 1, wherein the contacting pads are parallel to the cutting slot.
 11. The instrument of claim 1, wherein the contacting pads contact the femoral condyles at angle relative to the cutting slot and/or the mechanical axis.
 12. The instrument of claim 1, the body further comprising a passage.
 13. The instrument of claim 1, wherein the body includes at least one cross-member.
 14. The instrument of claim 1, wherein the body further comprises an anterior ridge extension.
 15. The instrument of claim 1, further comprising at least one surface contact confirmation slot.
 16. The instrument of claim 1, further comprising a distal trochlea grip.
 17. The instrument of claim 1, wherein each leg portion includes at least one paddle. 